This article explores some of the best practices that can be adopted
while using CVS as the configuration management tool in your software
projects.

1. Introduction

Men have become the tools of their tools.

--Henry David Thoreau (1817-1862)

This article outlines some of the best practices that can be adopted
when Concurrent Versions System is used as the configuration management tool in your software
project.

Concurrent Versions System (CVS) is an Open Source configuration management
tool that is now being looked at seriously by many commercial organizations as
a viable alternative to other commercial Software configuration management tools.

This spotlight on CVS has led to the inevitable question of best
practices for deploying CVS as the backbone SCM tool for large
software development projects. Having answered this question many times
verbally as a bunch of "gotchas" on CVS, it was time to put
down on paper some of the best practices that will work well for
CVS based projects.

This paper assumes that the reader is familiar with the
fundamentals of software version control. Including features like
branching, merging, tagging (labelling) etc., offered by modern version
control tools such as CVS

Further, This paper is not an introduction to CVS and its usage. There are
excellent articles available on the net for the same. This paper assumes
that the reader is familiar with CVS commands and is looking at
deploying CVS in his or her organization. Some of the popular
CVS related links that can provide CVS education are.

This document may be reproduced and distributed in whole or in part, in
any medium physical or electronic, as long as this copyright notice is
retained on all copies. Commercial redistribution is allowed and encouraged;
however, the author would like to be notified of any such distributions.

All translations, derivative works, or aggregate works incorporating
this document must be covered under this copyright notice. That is, you may
not produce a derivative work from this document and impose additional
restrictions on its distribution. Exceptions to these rules may be granted
under certain conditions; please contact the author at the address given
below.

In short, we wish to promote dissemination of this information through
as many channels as possible. However, we do wish to retain copyright on the
document, and would like to be notified of any plans to redistribute the same.

1.2. Disclaimer

No liability for the contents of this document can be accepted. Use
the concepts, examples and other content at your own risk. As this is a new
edition of this document, there may be errors and inaccuracies that may of
course be damaging to your system. Proceed with caution, and although this is
highly unlikely, the author(s) do not take any responsibility whatsoever.

All copyrights are held by their respective owners, unless specifically
noted otherwise. Use of a term in this document should not be regarded as
affecting the validity of any trademark or service mark.

Naming of particular products or brands should not be seen as
endorsements.

You are strongly recommended to take a backup of your system before
major installation and backups at regular intervals.

1.3. New Versions

This document is Version : 0.7.

The latest version of this document can be obtained from (In the order of latest version availability)

1.4. Credits

The list of people who have provided information and correction for this
paper in no particular order are.

Jens-Uwe Mager

Jorgen Grahn

Thomas S. Urban

Cam Mayor

Sally Miller

Niels Jakob Darger

1.5. Feedback

Feedback is most certainly welcome for this document. Without your
submissions and input, this document wouldn't exist. Please send your
additions, comments and criticisms to the following email address :
<vivekv at yahoo dot com>.

3. Using GUI Tools

The traditional interface available for CVS is the command-line client.
There has also been a slew of GUI client applications that can
"talk" to a CVS server. These GUI clients provide a
"point and click" interface to the CVS repository.

3.1. Use GUI CVS client

This paper recommends using such GUI clients during the initial
deployment of CVS in an organization.

Developers typically use integrated development environments that have
the CM tools integrated into them. These tools minimize the learning for the
developers about the intricacies of CVS usage and instead allow them to be
productive from day one. Developers who are accustomed to other CM tools will
find the CVS command-line interface daunting. The adoption and usage of
CVS can be improved by using GUI tools for CVS clients.

GUI tools for CVS are available at http://cvsgui.sourceforge.net/.
GUI interfaces are available for most of the popular platforms (Windows, Mac
and Linux). In addition, on the Windows platform there is an
SCC extension that allows integration of CVS as the
configuration control tool with popular IDE.

4. Developer Sandbox

The developer "sandbox" is where each developer keeps his
or her working copy of the code base. In CVS this is referred to as the
working directory. This is where they build, test and debug the modules that
they are working on. A sandbox can also be the area where the staging build
or the production build is done. Changes made in the work area are checked
into the CVS repository. In addition, changes made in the repository by
others have to be updated in the sandbox on a regular basis.

The best practices related to developers sandbox are:

4.1. Keep System clocks in Sync

CVS tracks change to source files by using the timestamp on the
file. If each client system date and time is not in sync, there is a
definite possibility of CVS getting confused. Thus system clocks must be
kept in sync by use of a central time server or similar mechanism.

CVS is designed from ground up to handle multiple timezones. As
long as the host operating system has been setup and configured correctly,
CVS will be able to track changes correctly.

4.2. Do not share the sandbox

Sandboxes have to be unique for each developer or purpose. They
should not be used for multiple things at the same time. A sandbox can be a
working area for a developer or the build area for the final release. If
such sandboxes are shared, then the owner of the sandbox will not be aware
of the changes made to the files resulting in confusion.

In CVS, the sandbox is created automatically when a working copy is
checked out for a CVS project using the cvs checkout
{project-name} command.

In very large projects, it does not make sense for the developers to
check-out the entire source into the local sandbox. In such cases, they can
take the binaries generated by the build team on a regular basis for all those
components of the application that is not changed by them and only check-out
the parts that are built by the developer.

For example, in a Java project, the build team can keep the results of
their last successful build in a standard location in the form of JAR files on
the network file servers. Individual developers will use a standard classpath
setup that has the network drives mounted on standard paths. Thus, the
developers will automatically get the latest version of the files as required
by them.

4.3. Stay in sync with the repository

To gain the benefits of working within a sandbox as mentioned above,
the developer must keep his or her sandbox in sync with the main repository.
A regular cvs update with the appropriate tag or branch
name will ensure that the sandboxes are kept up to date.

4.4. Do not work outside the sandbox

The sandbox can be thought of as a controlled area within which CVS
can track for changes made to the various source files. Files belonging to
other developers will be automatically updated by CVS in the developer's
sandbox. Thus the developer who lives within the sandbox will stand to gain
a lot of benefits of concurrent development.

4.5. Cleanup after Completion

Make sure that the sandbox is cleaned up after completion of work on
the files. Cleanup can be done in CVS by using the cvs
release command. This ensures that no old version of the files
exists in the development sandbox. As explained previously, pre-built
binaries from the build team can be used to ensure that all the parts of the
application are available to the developer without the need for a complete
compilation in the sandbox.

4.6. Check-in Often

To help other developers keep their code in sync with your code, you
must check-in your code often into the CVS repository. The best
practice would be to check-in soon as a piece of code is completed, reviewed
and tested, check-in the changes with cvs commit to
ensure that your changes are committed to the CVS repository.

CVS promotes concurrent development. Concurrent development is
possible only if all the other developers are aware of the ongoing changes
on a regular basis. This awareness can be termed as "situation
awareness"

One of the "bad" practices that commonly occur
is the sharing of files between developers by email. This works against
most of the best practices mentioned above. To share updates between two
developers, CVS must be used as the communication medium. This will
ensure that CVS is "aware" of the changes and can track
them. Thus, audit trail can be established if necessary.

5. CVS Server Configuration

This section deals with best practices for CVS server side setup and
configuration.

5.1. CVS access control

One of the important questions that I have been asked time and again is the
ability to have access control for files/folders/branches etc., within
the CVS repository for various users. Unfortunately CVS does not
come with a built in Access control capability but it does support a
rudimentary form of access control through the readers/writers files in
the CVSROOT repository. I have put together a set of scripts that use
the readers/writers files to provide a slightly useable version of access
control. This is available at http://cvspermissions.sarovar.org
as an Open Source project. Feel free to use it and let me know how it
works for you.

5.2. Server side scripting

Server side scripting refers to the ability to make CVS server
execute certain scripts when an event occurs. A common script that
helps is to verify that all cvs commits contain acomment entered by the
developer. The process involves setting up the
CVSROOT/verifymsg file to run a script when a file is
checked-in.

5.3. Server Notification

The CVS server can be configured to notify through e-mails in case
of a commit happening. This can be used to verify whether commits are
occurring during the course of a daily/release build. If such commits
occur, based on the project policy, the commits can be ignored or the entire
build automatically restarted.

6. Branching and Merging

Branching in CVS splits a project's development into separate,
parallel histories. Changes made on one branch do not affect the other
branches. Branching can be used extensively to maintain multiple versions
of a product for providing support and new features.

Merging converges the branches back to the main trunk. In a merge,
CVS calculates the changes made on the branch between the point where it
diverged from the trunk and the branch's tip (its most recent state), then
applies those differences to the project at the tip of the trunk.

6.1. Assign ownership to Trunk and Branches

The main trunk of the source tree and the various branches should have a
owner assigned who will be responsible for.

Keep the list of configurable items for the branch or trunk.

The owner will be the maintainer of the contents list for the branch or
trunk. This list should contain the item name and a brief description about
the item. This list is essential since new artifacts are always added to or
removed from the repository on an ongoing basis. This list will be able to
track the new additions/deletions to the repository for the respective branch.

Establish a working policy for the branch or trunk.

The owner will establish policies for check-in and check-out. The
policy will define when the code can be checked in (after coding or after
review etc.,). Who is responsible to merge changes on the same file and
resolve conflicts (the author or the person who recently changed the file).

Identify and document policy deviations

Policies once established tend to have exceptions. The owner will be
responsible for identifying the workaround and tracking/documenting the same
for future use.

Responsible for merge with the trunk

The branch owner will be responsible for ensuring that the changes in
the branch can be successfully merged with the main trunk at a reasonable point
in time.

6.2. Tag each release

As part of the release process, the entire code base must be tagged with an
identifier that can help in uniquely identifying the release. A tag gives a
label to the collection of revisions represented by one developer's working
copy (usually, that working copy is completely up to date so the tag name is
attached to the "latest and greatest" revisions in the
repository).

The identifier for the tag should provide enough information to
identify the release at any point in time in the future. One suggested tag
identifier is of the form.

release_{major version #}_{minor version #}

As one reader pointed out to me, a good practice here is to tag
the release first. Checkout the entire codebase using the tag, and then
proceed to go through a build / deploy / test process before making the
actual release. This will absolutely ensure that what "leaves the
door " is a verified and tested codebase.

6.3. Create a branch after each release

After each software release, once the CVS repository is tagged, a
branch has to be immediately created. This branch will serve as the bug fix
baseline for that release. This branch is created only if the release is
not a bug fix or patch release in the first place. Patches that have to be
made for this release at any point in time in the future will be developed
on this branch. The main trunk will be used for ongoing product
development.

With this arrangement, the changes in the code for the ongoing
development will be on the main trunk and the branch will provide a separate
partition for hot fixes and bug fix releases.

The identifier for the branch name can be of the form.

release_{major version #}_{minor version #}_patches

6.4. Make bug fixes to branches only

This practice extends from the previous practice of creating a
separate branch after a major release. The branch will serve as the code
base for all bug fixes and patch release that have to be made. Thus, there
is a separate repository "sandbox" where the hot fixes and
patches can be developed apart from the mainstream development.

This practice also ensures that bug fixes done to previous releases do
not mysteriously affect the mainstream version. In addition, new features
added to the mainstream version do not creep into the patch release
accidentally.

6.5. Make patch releases from branches only

Since all the bug fixes for a given release are done on its
corresponding branch, the patch releases are made from the branch. This
ensures that there is no confusion on the feature set that is released as
part of the patch release.

After the patch release is made, the branch has to be tagged using the
release tagging practice (see Tag each release).

7. Change Propagation

Change propagation practices explore how changes made to one version of
the application are migrated to other living versions of the application.

7.1. Merge branch with the trunk after release

After each release from a branch, the changes made to the branch
should be merged with the trunk. This ensures that all the bug fixes made
to the patch release are properly incorporated into future releases of the
application.

This merge could potentially be time consuming depending on the amount
of changes made to the trunk and the branch being merged. In fact, it will
probably result in a lot of conflicts in CVS resulting in manual merges.
After the merge, the trunk code base must be tested to verify that the
application is in proper working order. This must be kept in mind while
preparing the project schedule.

In the case of changes occurring on branches for a long period,
these changes can be merged to the main branch on a regular basis even
before the release is made. The frequency of merge is done based on certain
logical points in the branch's evolution. To ensure that duplicate merging
does not occur, the following practice can be adopted.

In addition to the branch tag, a tag called {branch_name}_MERGED
should be created. This is initially at the same level as the last release
tag for the branch. This tag is then "moved" after each
intermediate merge by using the -F option. This
eliminates duplicate merging issues during intermediate merges.

8. Software Builds

This section deals with the best practices for software builds. Build
is the process of creating the application binaries for a software release.
They are done in a periodic manner by the build teams to provide baseline
binaries for daily work.

8.1. Build Early and Build Often (BEBO)

A variation of this adage has been around in the Open Source
community called "Release Early and Release Often" for quite some time
albeit for a different reason. BEBO helps a development team identify
issues that can arise from checking in the wrong files. BEBO will address
integration issues at the application level that might have slipped passed
individual developer builds. It will also improve the team morale when they
see a working version of the application.

Builds must be done on a regular basis. There should be a dedicated
resource(s) assigned to do the same. The entire project team must be
trained to view the daily build as an important activity and not as a chore.
Builds must be completed without any failures on a regular basis. Build
failures must be a rare event and should be treated with utmost seriousness.
The project team should ensure that successful builds are top priority on
their agenda. The seriousness can be emphasised by setting up a penalty for
breaking the build.

Each build can be tagged in CVS using a standard naming convention.
This can help developers checkout a working version of the entire system
from daily builds for local development.

8.2. Automate build Process completely

Another key practice for software builds is to automate the build
process completely. The automation process must also include automatic
retrieval of the right source files from the CVS repository. This
ensures that the build process is completely repeatable and consistent. In
addition, the chances of a build with the wrong version of the application
source files are reduced to a large degree.

By automating the build process, the task of building often becomes
less burdensome.

8.3. All necessary files must be checked-in before build

This adage sounds trivial at first but this problem is very common
even with experienced development teams due to oversight. The problem of
oversight cannot be easily addressed since the onus is on the individual
developer to ensure that his or her file has been checked in. This practice
should be drummed into the team in the form of training and pre-build
announcements to ensure that the right version of source code is available
in the repository.

Automated build process as explained above will help in catching this
problem to a certain degree since they will automatically take the source
code from the CVS repository and perform the software build. Any missed
items will surface during the build process itself (makefiles etc.,) or
during the regression testing of the product (older version of the file
checked in).

A penalty based system can be setup to handle wrong check-in. Having a
kitty for a post project party to which each person who makes a wrong check-in
will contribute a fixed amount will act a good penalty system.

9. Institutionalize CVS in the Organization

Here we will look at the best practices for institutionalizing CVS
usage in the organization.

9.1. Implement Change Management Process

All organizations must implement a good Change management process
(CMP). A good CMP will define how changes are received,
recorded, tracked, executed and delivered. CVS provides version
control for your project. Change management addresses the "bigger
picture" of how enhancements and bugs are received, tracked and
closed. CVS will play a smaller but a very important part in this
entire picture. With a formal change management process in place in the
organization, tools such as CVS will be looked at as aiding this process
instead of acting as a general development overhead.

Change management is quite a vast topic that cannot be done justice
here. Please look up other sources of information on change management.

9.2. Make CVS Usage part of Objectives

To institutionalize CVS, it can be made as part of the performance
objectives for the developer to use CVS in the project. In addition, it
can also be made as part of the objective for the project manager to deploy
CVS in his or her project.

Compliance of this can then be reviewed as part of the appraisal cycle
for the employee.

9.3. Collect metrics on CVS usage

CVS usage metrics can be collected in terms of percentage of
deployment in the organization, project size handled etc., This information
will spur other line managers and program managers to look at CVS as a
tool that will aid them in their daily operations.

10. Best Practices in Action

The best way to explain the need for these best practices is by
putting together an example of a real world project scenario and show how
exactly will these best practices fit into the "bigger
picture". Also, a lot of readers have told me that the sections on
Branching and Merging
and Change Propagation will require examples for better
explanation. Listening to the readers is a Good Thing so I have
put together a particular project scenario and then create a series of
events to show how the best practices, if followed, would help is making
operations smoother.

10.1. Inception

Consider a software project where version 1.0 has just been put into
production and everyone is done celebrating. The next step is to start
working on the new features of the subsequent release. Also, the users of
the system have started to use it full-time and bug reports of various
levels have started to come in.

Before jumping into new enhancements or bug fixes, the best practices
for Branching and Merging should be followed. Few of
the important practices are Tag each release and
Create a branch after each release. These practices will
effectively established two "development environments",
one for regular enhancements and the other for bug fixes and minor
enhancements on the last release.

Let us assume that the release was tagged as

release_1_0

Then the branch was created with the branch name

release_1_0_patches

10.2. Development and Delivery

Now, we are ready for business. Let us examine the bug fixes and
enhancements track. Assume that there are three bugs of which two are of a
high priority that should be fixed right away (possibly within a week) and the
third can be delivered after some time (say after 4 weeks). In the
middle of this schedule there is a regular release scheduled in three weeks.
Considering that we have a busy month ahead, let us see how exactly we can
use the Best practices to ease the days ahead.

The timeline for the various release in the next month looks like this.

We have two teams, one working on the bug fix branch and another team
working on the features for the next release on the main trunk. These
teams must make sure that they start out with the right version in
their sandbox.

The bug fix team will check out using the command line

cvs checkout -R -r release_1_0_patches {project name}

The team that is working on the next release will use the command line

cvs checkout -R {project name}

As soon as the bug fix team completes the two top priority bugs, they
will update, verify a successful build and commit their changes to the bug
fix branch using the command line

cvs update -R -r release_1_0_patches {module name}

The team should perform a build at this point to verify that the
update did not break any code on the branch. Once the build is successful,
the branch should be committed back into the repository.

cvs commit -R -r release_1_0_patches {module name}

Build Early and Build Often : On a daily basis, each developer
will check in code to CVS and to ensure sanity of code, daily builds on
the bug fixed branch will be undertaken by checking out from
CVS on a clean environment and completely rebuilt. These daily builds
can be tagged in CVS using the following naming convention

build_1_1_yyyymmdd : for the branchbuild_2_0_yyyymmdd : for the trunk

The regular process of build-test-fix is followed to make a version
ready for delivery. The tag will help developers checkout a working copy of
the latest build as and when necessary.

When the source code is released to the outside world, two practices
have to be followed.

Tag each release : This ensures that the bug fix
release is tagged correctly and so can be traced out at a later point in
time if necessary.

11. Conclusion

These best practices are meant to help software teams get a head start
on using CVS for their development. The ideas presented here have to be
constantly reviewed and evolved. I would like this to be a growing and
evolving document. Please send your comments and ideas to
<vivekv at yahoo dot com>

0. Preamble

The purpose of this License is to make a manual, textbook,
or other written document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by
others.

This License is a kind of "copyleft", which means that
derivative works of the document must themselves be free in the
same sense. It complements the GNU General Public License, which
is a copyleft license designed for free software.

We have designed this License in order to use it for manuals
for free software, because free software needs free documentation:
a free program should come with manuals providing the same
freedoms that the software does. But this License is not limited
to software manuals; it can be used for any textual work,
regardless of subject matter or whether it is published as a
printed book. We recommend this License principally for works
whose purpose is instruction or reference.

1. Applicability and Definitions

This License applies to any manual or other work that
contains a notice placed by the copyright holder saying it can be
distributed under the terms of this License. The "Document",
below, refers to any such manual or work. Any member of the
public is a licensee, and is addressed as "you".

A "Modified Version" of the Document means any work
containing the Document or a portion of it, either copied
verbatim, or with modifications and/or translated into another
language.

A "Secondary Section" is a named appendix or a front-matter
section of the Document that deals exclusively with the
relationship of the publishers or authors of the Document to the
Document's overall subject (or to related matters) and contains
nothing that could fall directly within that overall subject.
(For example, if the Document is in part a textbook of
mathematics, a Secondary Section may not explain any mathematics.)
The relationship could be a matter of historical connection with
the subject or with related matters, or of legal, commercial,
philosophical, ethical or political position regarding
them.

The "Invariant Sections" are certain Secondary Sections
whose titles are designated, as being those of Invariant Sections,
in the notice that says that the Document is released under this
License.

The "Cover Texts" are certain short passages of text that
are listed, as Front-Cover Texts or Back-Cover Texts, in the
notice that says that the Document is released under this
License.

A "Transparent" copy of the Document means a
machine-readable copy, represented in a format whose specification
is available to the general public, whose contents can be viewed
and edited directly and straightforwardly with generic text
editors or (for images composed of pixels) generic paint programs
or (for drawings) some widely available drawing editor, and that
is suitable for input to text formatters or for automatic
translation to a variety of formats suitable for input to text
formatters. A copy made in an otherwise Transparent file format
whose markup has been designed to thwart or discourage subsequent
modification by readers is not Transparent. A copy that is not
"Transparent" is called "Opaque".

Examples of suitable formats for Transparent copies include
plain ASCII without markup, Texinfo input format, LaTeX input
format, SGML or XML using a publicly available DTD, and
standard-conforming simple HTML designed for human modification.
Opaque formats include PostScript, PDF, proprietary formats that
can be read and edited only by proprietary word processors, SGML
or XML for which the DTD and/or processing tools are not generally
available, and the machine-generated HTML produced by some word
processors for output purposes only.

The "Title Page" means, for a printed book, the title page
itself, plus such following pages as are needed to hold, legibly,
the material this License requires to appear in the title page.
For works in formats which do not have any title page as such,
"Title Page" means the text near the most prominent appearance of
the work's title, preceding the beginning of the body of the
text.

2. Verbatim Copying

You may copy and distribute the Document in any medium,
either commercially or noncommercially, provided that this
License, the copyright notices, and the license notice saying this
License applies to the Document are reproduced in all copies, and
that you add no other conditions whatsoever to those of this
License. You may not use technical measures to obstruct or
control the reading or further copying of the copies you make or
distribute. However, you may accept compensation in exchange for
copies. If you distribute a large enough number of copies you
must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated
above, and you may publicly display copies.

3. Copying in Quantity

If you publish printed copies of the Document numbering more
than 100, and the Document's license notice requires Cover Texts,
you must enclose the copies in covers that carry, clearly and
legibly, all these Cover Texts: Front-Cover Texts on the front
cover, and Back-Cover Texts on the back cover. Both covers must
also clearly and legibly identify you as the publisher of these
copies. The front cover must present the full title with all
words of the title equally prominent and visible. You may add
other material on the covers in addition. Copying with changes
limited to the covers, as long as they preserve the title of the
Document and satisfy these conditions, can be treated as verbatim
copying in other respects.

If the required texts for either cover are too voluminous to
fit legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto
adjacent pages.

If you publish or distribute Opaque copies of the Document
numbering more than 100, you must either include a
machine-readable Transparent copy along with each Opaque copy, or
state in or with each Opaque copy a publicly-accessible
computer-network location containing a complete Transparent copy
of the Document, free of added material, which the general
network-using public has access to download anonymously at no
charge using public-standard network protocols. If you use the
latter option, you must take reasonably prudent steps, when you
begin distribution of Opaque copies in quantity, to ensure that
this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you
distribute an Opaque copy (directly or through your agents or
retailers) of that edition to the public.

It is requested, but not required, that you contact the
authors of the Document well before redistributing any large
number of copies, to give them a chance to provide you with an
updated version of the Document.

4. Modifications

You may copy and distribute a Modified Version of the
Document under the conditions of sections 2 and 3 above, provided
that you release the Modified Version under precisely this
License, with the Modified Version filling the role of the
Document, thus licensing distribution and modification of the
Modified Version to whoever possesses a copy of it. In addition,
you must do these things in the Modified Version:

Use in the Title Page
(and on the covers, if any) a title distinct from that of the
Document, and from those of previous versions (which should, if
there were any, be listed in the History section of the
Document). You may use the same title as a previous version if
the original publisher of that version gives permission.

List on the Title Page,
as authors, one or more persons or entities responsible for
authorship of the modifications in the Modified Version,
together with at least five of the principal authors of the
Document (all of its principal authors, if it has less than
five).

State on the Title page
the name of the publisher of the Modified Version, as the
publisher.

Preserve all the
copyright notices of the Document.

Add an appropriate
copyright notice for your modifications adjacent to the other
copyright notices.

Include, immediately
after the copyright notices, a license notice giving the public
permission to use the Modified Version under the terms of this
License, in the form shown in the Addendum below.

Preserve in that license
notice the full lists of Invariant Sections and required Cover
Texts given in the Document's license notice.

Include an unaltered
copy of this License.

Preserve the section
entitled "History", and its title, and add to it an item stating
at least the title, year, new authors, and publisher of the
Modified Version as given on the Title Page. If there is no
section entitled "History" in the Document, create one stating
the title, year, authors, and publisher of the Document as given
on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.

Preserve the network
location, if any, given in the Document for public access to a
Transparent copy of the Document, and likewise the network
locations given in the Document for previous versions it was
based on. These may be placed in the "History" section. You
may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.

In any section entitled
"Acknowledgements" or "Dedications", preserve the section's
title, and preserve in the section all the substance and tone of
each of the contributor acknowledgements and/or dedications
given therein.

Preserve all the
Invariant Sections of the Document, unaltered in their text and
in their titles. Section numbers or the equivalent are not
considered part of the section titles.

Delete any section
entitled "Endorsements". Such a section may not be included in
the Modified Version.

Do not retitle any
existing section as "Endorsements" or to conflict in title with
any Invariant Section.

If the Modified Version includes new front-matter sections
or appendices that qualify as Secondary Sections and contain no
material copied from the Document, you may at your option
designate some or all of these sections as invariant. To do this,
add their titles to the list of Invariant Sections in the Modified
Version's license notice. These titles must be distinct from any
other section titles.

You may add a section entitled "Endorsements", provided it
contains nothing but endorsements of your Modified Version by
various parties--for example, statements of peer review or that
the text has been approved by an organization as the authoritative
definition of a standard.

You may add a passage of up to five words as a Front-Cover
Text, and a passage of up to 25 words as a Back-Cover Text, to the
end of the list of Cover Texts in the Modified Version. Only one
passage of Front-Cover Text and one of Back-Cover Text may be
added by (or through arrangements made by) any one entity. If the
Document already includes a cover text for the same cover,
previously added by you or by arrangement made by the same entity
you are acting on behalf of, you may not add another; but you may
replace the old one, on explicit permission from the previous
publisher that added the old one.

The author(s) and publisher(s) of the Document do not by
this License give permission to use their names for publicity for
or to assert or imply endorsement of any Modified Version.

5. Combining Documents

You may combine the Document with other documents released
under this License, under the terms defined in section 4 above for
modified versions, provided that you include in the combination
all of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your
combined work in its license notice.

The combined work need only contain one copy of this
License, and multiple identical Invariant Sections may be replaced
with a single copy. If there are multiple Invariant Sections with
the same name but different contents, make the title of each such
section unique by adding at the end of it, in parentheses, the
name of the original author or publisher of that section if known,
or else a unique number. Make the same adjustment to the section
titles in the list of Invariant Sections in the license notice of
the combined work.

In the combination, you must combine any sections entitled
"History" in the various original documents, forming one section
entitled "History"; likewise combine any sections entitled
"Acknowledgements", and any sections entitled "Dedications". You
must delete all sections entitled "Endorsements."

6. Collections of Documents

You may make a collection consisting of the Document and
other documents released under this License, and replace the
individual copies of this License in the various documents with a
single copy that is included in the collection, provided that you
follow the rules of this License for verbatim copying of each of
the documents in all other respects.

You may extract a single document from such a collection,
and distribute it individually under this License, provided you
insert a copy of this License into the extracted document, and
follow this License in all other respects regarding verbatim
copying of that document.

7. Aggregation with Independent Works

A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of
a storage or distribution medium, does not as a whole count as a
Modified Version of the Document, provided no compilation
copyright is claimed for the compilation. Such a compilation is
called an "aggregate", and this License does not apply to the
other self-contained works thus compiled with the Document, on
account of their being thus compiled, if they are not themselves
derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to
these copies of the Document, then if the Document is less than
one quarter of the entire aggregate, the Document's Cover Texts
may be placed on covers that surround only the Document within the
aggregate. Otherwise they must appear on covers around the whole
aggregate.

8. Translation

Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires
special permission from their copyright holders, but you may
include translations of some or all Invariant Sections in addition
to the original versions of these Invariant Sections. You may
include a translation of this License provided that you also
include the original English version of this License. In case of
a disagreement between the translation and the original English
version of this License, the original English version will
prevail.

9. Termination

You may not copy, modify, sublicense, or distribute the
Document except as expressly provided for under this License. Any
other attempt to copy, modify, sublicense or distribute the
Document is void, and will automatically terminate your rights
under this License. However, parties who have received copies, or
rights, from you under this License will not have their licenses
terminated so long as such parties remain in full
compliance.

10. Future Revisions of this License

The Free Software Foundation may publish new, revised
versions of the GNU Free Documentation License from time to time.
Such new versions will be similar in spirit to the present
version, but may differ in detail to address new problems or
concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing
version number. If the Document specifies that a particular
numbered version of this License "or any later version" applies to
it, you have the option of following the terms and conditions
either of that specified version or of any later version that has
been published (not as a draft) by the Free Software Foundation.
If the Document does not specify a version number of this License,
you may choose any version ever published (not as a draft) by the
Free Software Foundation.

How to use this License for your documents

To use this License in a document you have written, include
a copy of the License in the document and put the following
copyright and license notices just after the title page:

Copyright (c) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
A copy of the license is included in the section entitled "GNU
Free Documentation License".

If you have no Invariant Sections, write "with no Invariant
Sections" instead of saying which ones are invariant. If you have
no Front-Cover Texts, write "no Front-Cover Texts" instead of
"Front-Cover Texts being LIST"; likewise for Back-Cover
Texts.

If your document contains nontrivial examples of program
code, we recommend releasing these examples in parallel under your
choice of free software license, such as the GNU General Public
License, to permit their use in free software.